Sound reproducing system



Oct. 10, 1933.

B. E. G. MITTELL SOUND REPRODUCING SYSTEM 2 Sheets-Sheet 1 OriginalFiled Nov. 18 1925 Oct. 10, 1933. B; E. e. MITTELL scum) REPRODUCINGSYSTEM brigiual File Nov. '1 1925 2 Sheets-Sheet 2IIIIII,II'IIIIII'III'I'IIIIIII'IIIIIII(IIIIIIIIII'III'IIIIIIIJI PatentedOct. 10, 1933 UNITED STATES I -i, 929,92s

scum) REPRODUCING, SYSTEM Brenchley Ernest George Mittell, Iver,England, assignor, by mesne assignments, to Radio Corporation ofAmerica, New York, N. Y., a. corporation of Delaware ApplicationNovember 18, 1925, Serial No. 69,849,

and in Great Britain December 5, 1924. Renewed February 25, 1931 Claims.(01.177-1) This invention relates to sound reproducing systems such astalking machines or wireless receivers. I It is often desirable that thegenerator of 5 audio-frequency currents should be at a distance from thesound producing device, such a s-tele phone or loud-speaker. Forinstance in the case of a wireless receiver, with an outside aerial, thereceiver is preferably placed in the neighbouro hood of the point atwhich the aerial and earth connections are led in; whilst it may not beconvenient for the sound producing device to be operated in the sameroom. When a loudspeaker is used, moreover, it is preferable that itshould be placed at a distance from the listeners and it is alsodesirable that the tone quality and the volume of the sounds producedshould be regulable from the position of a listener.

According to the present invention, therefore, a sound reproducingsystem, comprising a unit in which audio-frequency electric currents aregenerated, such as a radioreceiver or talk ing machine recordco-operating with a microphone circuit, or an electro-mechanical deviceoperated directly by the record groove, a sound producing unit and acontrolling unit, which permits of the control of the other two unitsindependently of one another, has the said three units independentlymovable with regard to one another but interconnected electrically. The

control of the generating unit may be accom-' the valve filament circuitand the relay or relays may be energized from the battery which is usedfor heating the valve filaments.

One embodiment of the invention, in which the generator ofaudio-frequency currents is a single valve radio receiver, will bedescribed by way of example, with reference to the accompanying drawingsin which Fig. 1 shows diagrammatically the arrangement of the electricalcircuit. Fig. 2 shows a convenient form of wall plug and socketconnector.

Fig. 3 illustrates in more detail the relay in Fig. 1.

Fig. 4 shows the control .unit. Fig. 5 is a sectional view on the Fig. 6is a part sectional end view of the control unit.

Fig. 7 shows diagrammatically the arrange- 65 ment of a modification ofthe electrical circuit.

e AA of nected to earth.

Referring more particularly to Fig. 1 the thermionic valve 1 isconnected in the usualmanner to act as a detector and the output isconnected through the primary circuit of an output transformer 2. Theaudio-frequency currents generated in the secondary circuit of thistransformer are led through the connecting leads d and e. The valvefilament is heated by current from the battery 3 through the right handcontact 4 of the relay 5. The left hand relay contact 6 is connected tothe aerial and when contact is made on this side the aerialis con- Therelay is actuated by two solenoids 7 and 8 one terminalof the twosolenoid windings being connected together to contacts 27 and 28 ontherelay arm and to one terminal of the battery 3 whilst the otherterminals of the solenoid windings are connected to leads a and 0respectively. The other terminal of the battery is connected to lead b.The control unit 9 and the loudspeaker 10 are connected as shown .withthe receiving set by the leads ae. When, bypressing the left hand or onbutton of the switch 11, the leads a and b are connected together, theleft hand solenoid 7 is energized and the connections of the receivingset are then as shown in Fig. 1. In this case the filament circuit ofthe valve is closed and the set is consequently in action. When the lefthand button is released the contact is maintained by the spring catch12. If now the right hand button be pressed the leads b and c areconnected together and the solenoid 8 pulls down the relay arm, breakscontact 4 and makes contact 6. The filament circuit is thus opened andthe aerial is connected to earth. This contact is likewise maintained,after the button has been released, by the spring catch 12.

The control unit 9 comprises,- in addition to the switching arrangementfor putting the set into or out of action, means for controlling thevolume and tone quality of the sounds produced by the loud speaker 10.The volume control is obtained by varying the amount of resistance inseries or in parallel with the loud speaker and the control of qualityis obtained by varying the electrdstatic capacity in series or inparallel with the loud speaker. The variable capacity and resistanceemployed for tone and volume control are preferably either bothconnected in-series or both in parallel with the loud speaker as by thismeans the number of leads required to the lea necessary when bothresistance and capacconnections.

Referring now to Figs. 4. 5 and 6 which show and loud speaker to beplaced in connection with the receiving set. The five leads a-e mayconveniently be formed into a single five core cable with which thebuilding, in which the system is to be used, is wired and the five leadsmay be connected at suitable points to wall sockets 13. This particularsocket is adapted for use where the capacity and resistance used forcontrolling purposes are placed in series with the loud speaker and inwhich it is necessary that the loud speaker be connected to the samesocket as that to which the control box is connected and the socket 14:for. the loud speaker connecting plug 15 is consequently providedintegral with the main socket 13. The leads a-d are connected with fourterminals of the main socket 13 as shown in Fig. 2 and lead 6 isconnected with one terminal of the loud speaker socket 14, the otherterminal of the loud speaker socket being connected to the fifthterminal of. the main socket. The control unit 9 is provided with aflexible cable 16 terminating in a five pin plug 17 adapted to engagewith the main socket 13. The loud speaker 10 is likewise provided with aflexible cable 13 terminating in the two pin plug 15.

If the controlling resistance and capacity be provided in parallel withthe loud speaker the leads Ze may be connected directly to the terminalsof the sockets 13 which are adapted to connect with leads f and g of thecontrol unit respectively and also with any desired number of separatesockets suitable to receive the loud speaker plug 15. In this case thecontrol unit and loud speaker may each be plugged into any desired oneof the corresponding sockets provided.

In Fig. 3 is shown in more detail the relay 5 of Fig.- 1. This consistsof a T-shaped member 19 rotatably mounted upon a pin 20. Two soft ironplungers 21 and 22 are pivotally attached to the two upper ends of themember 19 and enter the solenoids 7 and 8 respectively. The solenoidsare each provided with iron yokes 23 and iron cores 24. The lower end ofthe member 19 is provided with a roller 25 which engages with a cam 26on thespring catch 12. A spring carrying two contacts 27 and 28 is fixedto the top of the member 19, the contacts being adapted to engage andmake electrical contact with fixed contacts 6 and 4 respectively. Oneend of the winding of each of the solenoids "7 and '8 is connected totheterminal 29 and to the contacts 27 and 28 whilst the other two ends ofthe windings are connected to terminals a and 0 respectively. a

When the winding of the solenoids is ener gized the plunger 22 isattracted downwards into the position shown in Fig. 3 and electricalconnection is made between contacts 27 and 6. The spring catch 12ensures that this contact is maintained when the current through thesolenoid is interrupted and it is therefore only necessary for currentto flow momentarily through the coil to eflect the desired change inalong the resistance elements.

the control unit 9 of Fig. 1 in more detail, the switch, indicated by 11in Fig. 1, comprises two bell crank levers 30 and 31 which are rotatablymounted on a pin 32. The levers are actuated by press buttons 33 and 34respectively and are normally pressed against the press buttons by aspring35. The levers are adapted to make contactwith contacts 36 and 37respectively which are insulated from one another and connected to leads0 and,a respectively, the levers 30 and 31 being connected to the leadI). The upper arms of the levers 30 and 31 are adapted to engage with apin 38 mounted on a slider 39 which carries upon its upper surface theinscriptions on" and "011; When the button 34 is pressed the slider 39is moved to the right and when contact is made between the lever 31 andthe contact 87 the word on is visible through an aperture 40 in thecontrol unit casing. The slider is held in this position by frictionuntil the button 33 is pressed and the lever 30 then moves the slider tothe left and the word off 7 becomes visible through the aperture 40.

The variable resistance which provides volume control consists of anumber of resistance elements 49 mounted upon a bobbin 41 and connectedin series, the free terminal or the first element being connected to'the:left hand contact 50 and the lead 1 and the'remaining contacts 50 beingconnected to suitable tappings The contact arm 42 is fixed to arotatably mounted hollow shaft 43, provided with a control knob 4.4, andis adapted to slide over the contacts 50 and make electrical contacttherewith.

The condensers 51, which provide control of quality, each, have one oftheir terminals. connected to common bars 45 and to lead g, their otherterminals 52 being connected respectively to contacts 53. A contact arm46 is fixed to a shaft 47, provided with a knob 48, which is rotatablewithin the shaft 43 and in electrical connection therewith. Thisconnection is the one common to the resistance and capacity which can beseen in Fig. 1.

The contact arm 46 may bereplaced by. a broad contact arm which isadapted to make contact with any desired number of the contacts 53 atone time. By this means there are no drops in the value of the capacityas the arm is rotated over the contacts but as it is rotated to makecontact with an additional contact the value of the capacity connectedto that contact is added to that previously in circuit. The values ofthe individual capacities required for a given total capacity is. lesswith this arrangement than with that shown in the drawings. I

The values of the capacities used will vary with the loud speakeremployed and with the inherent capacity of the house wiring and of theoutput transformer. The value of the inherent capacity can, however,always be adjusted to a' definite fixed amount to,suit the'control unitby the insertion of suitable capacity in series or in parallel with thewiring. If, for example, the loud speaker requires a parallel capacityof between 0.005 and 0.01 microfarads and the inherent capacity is 0.02microi'arads whilst the control unit gives a series capacity of fromzero to 0.01, a permanent series capacity of 0.02 microiarads, must beinserted and the control unit will then cover the desired range.

The knobs 44 and 48 maybe provided with suitable indexes adapted toregister with scales carried upon the upper surface of the control unit.This is, however, not shown in the drawings.

It must be noted that alteration or the pure resistance in series orparallel with the reproducer will alter the frequency characteristic,and therefore the quality, in addition to the volume.

In some cases, particularly where reproducers of low impedance are usedand consequently the capacity of the line becomes of less importance,

it is sufiicient to" provide only one 01 the two forms of controlmentioned for example the volume control.

When the invention is applied to a talking machine, an electricalpick-up device or micro phone is substituted for the usual sound box andthe audio-frequency currents may then be amplified by a thermionicamplifier which may be controlled from a distance by a control unit. Thecontrol unit may also actuate electrically any of the various controlswhich have been proposed for use in magazine talking machines.

The number of wires which run between the unit in which audio-frequencycurrents are generated and the control unit and reproducer may of coursebe varied as desired. It has been found possible, in the arrangementdescribed, to reduce the wires from me to four, for example .by makingthe receiver earth connections through a condenser of large capacity andusing line at in place of lines a, b, or c.

I claim:

1. A sound reproducing system comprising radio receiving unit, a soundproducing unit and a single controlling unit having means forcontrolling the other two units independently of one another, and havingthe said three units independently movable with regard to one anotherbut interconnected electrically, and wherein said radio receiving unitcomprises a thermionic valve and wherein said single controlling unitcomprises means for making and breaking the file.- ment circuit of saidthermionic valve and means adapted to connect the aerial of said radioreceiver to ground when the filament circuit of trical condensers, aplurality of contact studs 'operatively connected to said condensers,and a rotary switch arm adapted to make electrical contact withsuccessive studs while still maintaining contact with those studs withwhich it has already made contact to vary the capacity of said soundproducing unit.

8. In a sound producing system wherein a unit in which audio-frequencyelectric currents are generated is associated with a sound producingunit, the combination with said units of a controlling unit forindependently controlling the same, said controlling unit comprising aplurality of electrical condensers operatively connected with said soundproducing unit, a plurality of resistance elements electricallyconnected to said sound producing unit, a plurality of contactsassociated with said-condensers and resistance elements, and a pair orcoaxially mounted and electrically connected switch arms adapted to bemoved independently and selectively into engagement with said contacts.

4. In a sound reproducing system wherein a unit in which audio-frequencyelectric currents are generated is associated with a sound producingunit, the combination with said units or a controlling unit forindependently controlling said two first named units, said controllingunit including a plin'allty 0! press button switches, a relay embodyinga plurality or exciting coils and an armature associated with saidswitches, the actuation or one or said switches being adapted to closethe circuit oi one of said exciting coils and actuate said armature,'andmeans for maintaining said armature in the position into which it hasbeen moved by the actuation of said 5. In a sound reproducing systemwherein the unit for generating audio-frequency electric currents isassociated with a sound producing unit, the combination with said unitsor a controlling unit comprising a plurality of press button switches,means actuated by said button switches toindicate the button which waslast pressed, a relay embodying a plurality or exciting coils and anarmature operatively connected with said button switches, and means formaintaining said

